I've heard it likened to The Force Awakens: a soft remake masquerading as a sequel that's inferior to the original in every way, but possibly still entertaining as spectacle if you don't compare them.
I saw it last night and think that's fair. I'd say where Gladiator was a historically adjacent journey, Gladiator II was a complete historical fabrication and a sprint. The story in the sequel is more complicated but not for the better as they just have to rush the pace a lot more and not flesh things out. For example the other gladiators on the team were basically just recurring background characters, and he went from slave to champion in just a couple of days. Also while I was not nearly as well versed in Roman history when Gladiator came out, as I learned about it (The History of Rome podcast by Mike Duncan) when I came to the part I was able to put into context when the movie was set. So now that I am knowledgeable in Roman history, the complete lack of authenticity bugged me a lot more here.
I haven't seen Gladiator in a long time but it's a memorable classic. Gladiator II was entertaining but not something you really remember after watching it. And one thing that bugs me that's common in today's movie was the soundtrack, which was completely forgettable here except for the parts where the dropped in something from the original. On the positive side of things, Denzel Washington was great and really stole the show.